1. Field of the Invention
The present invention relates to automated noninvasive blood pressure monitoring. Specifically, it relates to methods, systems, and apparatuses for calculating noninvasive blood pressure and associated clinical parameters which employ the oscillometric method and automatic heart rate calculation.
2. Description of the Related Art
Various techniques have been proposed for noninvasive measurement of blood pressure. A technique employed by many commercial monitoring systems is based on the well-known “oscillometric” method. The oscillometric technique requires measuring the pulsations induced by the artery as the cuff is inflated and deflated. As the cuff inflates to a predetermined pressure above the systolic blood pressure, the artery of the arm is compressed and the passage of the blood is stopped. At this point no oscillometric pulsation is sensed by the device. Then, the cuff is gradually deflated and the oscillations become increasingly significant until the pulse pressure in these oscillations reaches a maximum amplitude. The point at which the oscillations have a maximum amplitude corresponds to the mean arterial pressure (MAP) on the cuff pressure signal. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) are then calculated empirically based on the MAP as two different percentage points before and after the MAP point. Numerous blood pressure measurement-related inventions have been proposed based on the underlying principle of the oscillometric technique such as U.S. Pat. Nos. 4,984,577, 7,300,404, 7,153,269, 7,041,060, 7,052,465, 7,118,535, 7,311,669, and many others. Prior-art references of the oscillometric technique typically rely on performing some type of beat detection in order to calculate the pulse pressure in the oscillometric signal and determine the heart rate, and rely on two fixed MAP-based thresholds to determine SBP and DBP. Improved methods can be obtained by eliminating the need for automatic detection algorithms and by incorporating vector-based thresholds that increase the accuracy of the blood pressure measurement system. Additionally, improvements on the basic oscillometric method can be made in order to increase the robustness to motion artifact.